Congenital melanocytic naevi and pigmentary birthmarks

A six-week-old girl is brought to the general practitioner by her mother, who has noticed a large dark-brown patch covering most of the upper back since birth. The patch is well-defined, slightly raised, and covered with fine dark hair, and there are about a dozen smaller dark-brown spots scattered over the rest of the back and the shoulders. The girl was born at term, she is feeding and growing well, and her development is on track. On examination, the patch on the upper back measures fourteen by sixteen centimetres and sits over the thoracic spine, with the surrounding satellite nevi over the back, the shoulders, and the upper arms. The head circumference is on the fiftieth centile, the fontanelle is soft, and the neurological examination is normal. This is a large congenital melanocytic naevus on the posterior axis with multiple satellite nevi — the pattern that raises the concern for the neurocutaneous melanocytosis and warrants the referral to the specialist CMN service and the consideration of the CNS imaging. [2] [6]

Overview & Definition

The congenital pigmentary birthmarks are the coloured skin lesions present at birth or appearing within the first year of life, and they are among the commonest findings of the newborn and the infant skin examination. The group spans the benign and the commonplace — the dermal melanocytosis of the Mongolian spot that fades by the age of four, the isolated cafe-au-lait macule, and the small congenital melanocytic naevus — to the rare and the serious — the giant congenital melanocytic naevus with the neurocutaneous melanocytosis, and the syndromic pigmentary pattern of the neurofibromatosis type 1. The skill of the paediatric clinician is to recognise the lesion, to stratify the risk, and to identify the small number of children who need the specialist service and the surveillance. [10]

The congenital melanocytic naevus (CMN) is the hamartomatous proliferation of the melanocytes that is present at birth or appears within the first year as the tardive CMN. It is the lesion that carries the melanoma risk, and that risk is the reason the CMN is distinguished from the other pigmentary birthmarks and managed with the surveillance. The CMN is classified by the size — and specifically by the projected adult size, the size the lesion will reach when the child is fully grown — because the size is the single strongest correlate of the melanoma risk and of the risk of the neurocutaneous melanocytosis. [1] [2]

The clinical importance of the pigmentary birthmarks lies in three things. The first is the melanoma risk of the CMN, which is concentrated in the large and the giant lesions and which shapes the surveillance. The second is the neurocutaneous melanocytosis, the rare complication of the large posterior-axis CMN with the satellites, in which the melanocytes populate the leptomeninges and carry the risk of the hydrocephalus and the melanoma of the central nervous system. The third is the syndromic significance of the cafe-au-lait macule and the hypopigmented macule, which point to the neurofibromatosis type 1, the McCune-Albright syndrome, and the tuberous sclerosis when the pattern is recognised. [6] [10]

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2. [2]Krengel S, Scope A, Dusza SW, et al. New recommendations for the categorization of cutaneous features of congenital melanocytic nevi. Journal of the American Academy of Dermatology, 2013.PMID 22982004
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